Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to radar detection systems, and more particularly to a system and method for identifying hidden objects obscured beneath a layer of snow.
2. Description of the Background Art
Detecting objects whose visibility is obscured by accumulated snow has posed a challenge in a number of application areas. Snow removal equipment, such as snow blowers and snowplows, along with other types of vehicles traversing roads or other areas heavily laden with snow, are often subject to collision and damage from guardrails, vehicles, signage, fences, garbage, and other assorted objects hidden by the snow. Other applications exist for detecting objects beneath a layer of snow, such as for use by searchers and law enforcement personnel, which must meet the challenge of finding persons, or objects, which may be buried under one or more accumulated layers of snow. Currently, equipment operators, individuals performing a search, and other individuals subject to activity within snow laden environments have no readily available means of gathering information and images about objects which are otherwise hidden by layers of snow.
Mechanical detectors are conventionally utilized in snow removal equipment for detecting objects, and are an attempt to reduce the amount of damage caused by encounters with obstacles hidden beneath the snow. It will be appreciated that objects buried in the snow may pose a hazard to equipment, such as being ingested by a snow blower when clearing a snow bank. Furthermore, the snow removal equipment may damage items, such as vehicles, the visibility of which is obscured by one or more layers of snow. Detection using a mechanical detector requires a portion of the mechanical detector to make contact with the obstacle, and the technique is not capable of providing an image, or other information, as to the nature of the obstruction, or about those parts of the obstruction which are still hidden beneath the snow. It should be appreciated that the required contact force for such a mechanism is necessarily high so that the unit is not disengaged upon contact with packed snow or icy patches. A high contact force of this nature would often be sufficient to damage trapped vehicles, signage, and so forth. Therefore, mechanical sensing does not provide for the detection of an object prior to contact, and it does not provide imaging of objects hidden beneath the snow. It should also be appreciated that many obstacles typically encountered in a number of applications would not trigger a mechanical detection mechanism, however, they could still represent a significant threat, such as to a moving snowplow vehicle. For example, a number of-smaller objects can be ingested by a rotary plow which may completely entangle the rotary mechanism thereby rendering it inoperative, while requiring extensive time, effort, and expense to repair.
Techniques for detecting individuals buried under avalanches generally utilize forms of cooperative sensing, such as requiring the use of an active transmitter or passive transponder by a buried individual. It will be appreciated that cooperative means are not appropriate when the detection of vehicles, trees, storage containers, snow chains, culvert materials, and other inanimate objects is necessary, or when a priori equipping of an individual with a transmitter is not possible. One proposed non-cooperative technique utilizes at least two, and typically numerous, receiving antennas configured to detect reflected RF energy to determine the direction of the target, however, it is incapable of providing sufficient resolution for imaging obstructions buried in snow.
Techniques are being deployed by the military for obtaining images of the soil by using ground-penetrating radar (GPR). The use of GPR requires transmit/receive antennas which are in contact, or in close proximity, with the ground. Thus, obtaining images using such a system requires the physical relocation of the GPR antenna over the ground area. GPR systems are intended to image objects on or very near the surface of sand or soil, and are not configured for detecting objects within a snow bank, or other accumulation of snow, wherein detecting objects to a depth of about two meters is necessary. It will be further appreciated that the lack of homogeneity within a snow environment presents unique challenges for an object sensing technique. GPR applications generally require complex signal processing to be performed to eliminate unwanted signals and to provide for imaging of the results, as a result of which real-time signal and image processing may not be feasible or cost-effective in these cases. In addition, these GPR systems have been geared toward military applications, such as the detection of unexploded ordinance (UXO). Aside from the aforementioned difficulties, the GPR systems also suffer in the area of system complexity, size, and cost, thereby reducing their applicability such as for civilian transportation applications.
Therefore, a need exists for an apparatus that provides for the detection and imaging of objects obscured beneath a layer of snow which is not subject to the limitations as outlined above. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed solutions.
The present invention is a non-contact system and method for detecting and/or imaging of objects which are obscured beneath snow, or materials of similar composition. The snow penetrating radar system and method presented herein is applicable to a number of applications and is particularly well-suited for search and rescue situations, and for the prevention of damage to machines operating in snow, such as snow removal equipment. The-system maybe implemented as a compact low-cost unit that may be mounted upon a-movable platform, such as a motor vehicle, aircraft (i.e. helicopters), or a mobile individual (i.e. person on foot or on horseback). By utilizing the present invention on snow removal equipment, collisions with objects hidden beneath the snow may be prevented, and the damage resulting from the ingestion of small objects into the blade mechanism of rotary snowplows, (xe2x80x9cblowersxe2x80x9d) can be circumvented. The ability to reconstruct object images for identifying objects obscured by snow allows-for the rapid scanning of a snow scene, for example an avalanche site, from several meters above the scene while detecting, locating, and possible victims. The ability to discern victims from debris can facilitate victim rescue operations in snow-laden areas.
The method utilized within the invention for detecting objects beneath a layer of snow is conceptually similar to the ground-penetrating radar utilized by the military. However, the system and method of the present invention does not require the physical movement of an antenna over ground areas to be imaged, and is capable of imaging obscured objects without the need of pulsed radar phase measurements in combination with expensive and complicated digital signal image processing techniques to reconstruct an object image. The present system and method is configured to reconstruct real-time multiple frames per second non-specular object images without making contact with the objects and regardless of the condition of the overlying snow, such as powder, packed snow, very dense snow, dry snow, wet snow, and combinations thereof.
Imaging through snow with the present system allows scanning of a scene in from one to three dimensions, with the preferred use of two dimensions such as azimuth and elevation. The radar utilized herein provides a continuous wave output in preference to the conventional pulsed radar systems which provide imaging through the registration of phase differences. Objects may be registered from several meters distance while providing sufficient resolution to detect objects which could pose a danger to snow removal equipment, and the like.
The system generates a narrow radio-frequency (RF) output signal beam, preferably at a microwave frequency, whose output beam is scanned across a target scene by any conventional RF scanning mechanism. It will be appreciated that an RF beam may be scanned using a number of methodologies, including electronic beam scanning, mechanical and electromechanical scanning of antenna assemblies or deflector assemblies. In any of these approaches the beam width may be optionally modified by passing the beam through one or more lenses, such as a negative refraction index lens to narrow the beam width toward the target area which may contain one or more objects obscured beneath a layer, or layers, of snow. The RF energy penetrates through the snow and will be reflected from underlying solid objects. A receiver antenna array receives and sums the RF energy reflected from the underlying objects. The detected RF signal is conditioned within the receiver, by filtering and amplitude compensation, prior to conversion of the magnitude-only signal to an object detection signal for use by an annunciator which indicates or displays information about said object from said object detection signal. In the process of converting the detected RF signal to an object detection signal, the position along the scan path which determines the direction of the transmitted beam toward target area, is correlated with the amplitude (magnitude) of the detected RF so that the resultant spatial information signal preferably includes both position and amplitude information based on the reflected RF signal received from the target area. The correlation is preferably performed by combining the magnitude and direction information into a single object detection signal which drives an image display. For example, when directed to an image display unit the characteristics of pixels are modulated, such as according to intensity and/or color, within the object detection signal according to the magnitude of the detected RF signal, while the position of the pixels on the display unit is determined in relation to the direction at which the corresponding RF signal beam was transmitted toward the target area. It will be appreciated that the direction of the transmitted RF beam toward the target area may be determined in response to the position of a mechanical or electromechanical scanning system, or depending on phase relationships or field intensities in the case of electronic beam scanning. In the case of a mechanical or electromechanical scanner assembly which modulates either the antenna direction or modulates beam deflection from an antenna assembly, the scan path may be registered in response to the physical position of one or more mechanical positioners along a given path. The annunciator may comprise a display unit, audio alert device, haptic feedback device, or other feedback units, utilized either singly or in combinations thereof, to indicate the presence, position, and/or distance of objects within the target area. It will be appreciated that the use of a display unit for annunciating is generally substantially preferred as it provides reconstruction of object images from which an operator can intuitively glean a wealth of information. The use of a display unit may be optionally augmented with audible, tactile, haptic, and other visual alerts which may be generated in response to the condition of objects in the target area. The use of haptic feedback for distance warning has the added benefits of being noticeable to an operator whose visual focus is directed outside the vehicle and it remains noticeable despite severe noise, such as generated by a mechanical snow blower. The haptic feedback is preferably coupled to the operator seat or operator controls for easy detection by the operator during use of the system on a mobile platform. The complexity and cost of the present system is minimized by the use of continuous wave output, wherein complex phase processing electronics are not necessary. In addition, the beam scanning mechanism is capable of scanning the RF output signal beam across a target surface without the necessity of physically moving a transmitter or detector array over the ground surface in the target area. Three-dimensional images may be captured by utilizing more than one RF source which may be scanned over the target surface from slightly different angles.
Synthetic aperture imaging techniques may be utilized to combine multiple reflection images captured from slightly differing vantage points into images having a higher pixel resolution than the original reflection images. It will be appreciated that the technique requires knowledge of the relative positions from said object to which the images were obtained, as may be provided by movement registration or the receipt of position information such as high accuracy GPS coordinates. Furthermore, the transmitter and detector positions may be spatially modulated to provide capturing multiple spatially displaced images from a stationary.location.
An object of the invention is to provide a system and method for acquiring images of objects obscured by a layer of snow.
Another object of the invention is to provide a system and method which can be utilized from a moving platform, such as mounted on a vehicle, aircraft, or mobile individual.
Another object of the invention is to provide an imaging apparatus that operates through snow regardless of its condition, such as powder, packed snow, very dense snow, dry snow, wet snow, and combinations thereof.
Another object of the invention is to provide an imaging system for use in snow that can detect objects from a distance of at least one to two meters.
Another object of the invention is to provide a hidden object imaging apparatus for use in snow that does not require the physical movement of an antenna over the surface of the snow in order to generate object images.
Another object of the invention is to provide scanning of objects beneath a layer of snow, or similar composition, by reflecting continuous wave RF energy from the surface of hidden objects.
Another object of the invention is to provide real-time output with multiple frames per second output.
Another object of the invention is to provide non-specular images having high image quality.
Another object of the invention is to provide object imaging without the necessity of extensive signal processing.
Another object of the invention is to provide a method of imaging objects beneath snow which can be implemented at low cost.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.